Move code from server() to Shiny modules

[ohjakobsen]

The server() function is currently quite bloated. It should be split into modules for better readability and quality control. This will also facilitate the ability to provide separate apps for specialised tasks while keeping the functionality within the pioneeR app. The following functions should be split into modules:

• File upload
• Data selection (old conditional UI file)
• DEA
• Bootstrap
• Malmquist

All modules should be kept in a mod_*.R file with a *_ui() and *_server() function. All server modules should return a reactive object that can be passed to other modules if needed.